The present invention relates generally to shielding apparatus for electromagnetic shielding, and, more particularly, to an electromagnetic shield having a convective, heat-dissipative surface for dissipating heat generated during operation of the electrical circuit.
High frequency electromagnetic signals are generated during operation of an electrical circuit containing a high frequency oscillator. These electromagnetic signals are a byproduct of normal operation of the electrical circuit, and are undesirable as the generated signals can interfere with normal functioning of other electrical circuits. Such interference, and the unwanted effects thereof, is well known to users of electronic equipment.
In order to minimize the effects of the interference, electromagnetic shielding material is oftentimes positioned to cover electrical circuits. The shielding material absorbs the electromagnetic signals generated by the electrical circuits which the shielding covers, as well as signals generated by other circuits. The shielding material is frequently comprised of a metallic, or other electrically conductive, material, and may take the form of a planar surface or a housing completely enclosing the electrical circuit.
One known type of shield for shielding electromagnetic energy consists of a metallic plate member positioned over the electromagnetic energy-producing electrical circuit. The metallic plate member absorbs the electromagnetic energy generated during operation of the circuit. Side flanges extend downwardly from the plate member, and a conductive braid material, or conductive-rubber material, supported by the flanges, electrically connects the shield to the electrical circuit. Typically, the shield is electrically connected to the ground plane of the electrical circuit, or some other such common reference plane; otherwise, the shield can function as an antenna for receiving electromagnetic energy transmitted by other electrical circuits.
The braid, or conductive-rubber material, is physically connected to the flanges extending downwardly from the plate member by inserting the braid, or conductive-rubber material, into an indentation formed in bottom surfaces of the flanges. Use of the braid, or conductive-rubber material, is desired in order to ensure that an electrical connection between the shield and the circuit is maintained.
Another byproduct of normal operation of an electrical circuit is thermal energy, i.e., heat. If not dissipated, a buildup of heat can cause abnormal operation of the electical circuit, and can even damage the component elements of the circuit. Therefore, a means for dissipating heat is oftentimes positioned proximate to the electrical circuit. For example, thermally conductive materials forming heat sinks containing convective surfaces are oftentimes positioned proximate to an electrical circuit to permit dissipation of heat energy conducted thereto.
Electronic equipment containing one or many electrical circuits is being increasingly miniaturized in order to permit the equipment to be housed in ever-smaller packages. In order to permit such miniaturization, the aforementioned electromagnetic shielding apparatus and heat dissipation apparatus must similarly be miniaturized to fit in the ever-smaller packages. For instance, electromagnetic shielding apparatus has been developed which also functions as a heat sink to dissipate heat generated during operation of an electrical circuit.
One such example of electronic equipment which has been increasingly miniaturized is a handheld, portable radiotelephone. As the radiotelephone package is increasingly miniaturized, the electromagnetic shielding apparatus and heat dissipation apparatus housed within the radiotelephone housing must be commensurately miniaturized.
Shielding apparatus, such as the shield described hereinabove, may be used in a portable radiotelephone. Design constraints, however limit further miniaturization of such a shield. The metallic plate member forming a portion of the shield and flange projecting therefrom are typically constructed by a die-cast or extrusion process. While the dimensions of the flange portions formed during a die cast process may be as thin as 0.025 inch, or even thinner, the flange must be wide enough to form a channel to support the braid or conductive-rubber material. Because the braid or conductive-rubber material is connected to the bottom of the flange portion by forming an indentation into the bottom end of the flange portion, and because the braid or conductive-rubber material is of dimensions of 0.015 inch, the width of the indentation formed in the bottom end of the flange portion must be of a corresponding width. The side walls forming the indentation must be of dimensions of 0.025 inch for reasons of process limitations, and the resultant flange width must be, accordingly, at least 0.065 inch. Because the flange portions of the shield typically extend about the perimeter of the electrical circuit, the total flange area in both the widthwise and the lengthwise direction of the shield plate must be two times 0.065 inch, or 0.130 inch. As mentioned hereinabove, because the handheld radiotelephone is becoming increasingly miniaturized, this area required for the flange portions of the shield plate is increasingly becoming a design constraint limiting further miniaturization of the radiotelephone package. The size requirements of shielding apparatus for electrical circuits of other electronic devices is similarly becoming a design constraint limiting further miniaturization.
Accordingly, improved means and methods for shielding and for dissipating heat are therefore required in order to permit increased miniaturization of electronic equipment.